Thanks for your answers! Actually, i'm not in australia but in france and here, celica's are not really common so the only solution i got is to order new parts from the toyota dealer (he told me they still do it... is that true?).
To answer a few questions : the speedo only goes up to 99 999km like yours... but i know it already did a hundred so... and i do believe the carbs are horizontals (they are "directly" mounted to the cylinder head without an elbow... am i right?)
I'm waiting for others replies everybody tell me his celica story!
Thanks